Convolutely wound tubes are commonly employed as cores about which extended lengths of carpet, paper, and other sheet material are wrapped into large spiral wound rolls for transport and storage. Such tubes typically are fabricated by drawing paperboard from a large supply reel, moving it along its length through an adhesive applicator, cutting it across its length to form a sheet of paperboard, securing one edge of the paperboard sheet in the longitudinal slot of a cylindrical mandrel, and rotating the mandrel to wind the paperboard about the mandrel into an elongated tubular configuration. The adhesive bonds successive layers of the tube walls securely together providing a convolutely wound paperboard tube that is economical to produce and that exhibits strength and bending resistance superior in some instances to more expensive spiral wound and other types of tubes.
The just described process has been employed for many years in the fabrication of convolutely wound tubes. Although the process has proven satisfactory, it nevertheless has long been plagued with persistent problem that heretofore has evaded a satisfactory solution. Specifically, the thickness and rigidity of the paperboard from which tubes are wound tends two cause the trailing edge of the paperboard sheet to resist conforming to the outside contour of the tube and to spring away from the tube after the tube is wound. The adhesive that is applied to the paperboard generally has insufficient holding capacity to secure this trailing end in place as the adhesive cures.
Prior solutions to this persistant problem generally have included treatment of the trailing edge of the sheet prior to winding of the trailing end of the sheet onto the tube to render the edge more pliable or flexible and thus more easily conformable and securable to the outer surface of the tube. One widely accepted solution employees a sanding device known as a skiver havintg a moving abrasive belt that rides on an edge of the paperboard material as it is drawn from its supply roll. The sanding belt abrasively removes material from the edge of the paperboard to render the edge signficantly thinner and thus much more pliable and conformable than it otherwise would be. This sanded flexible edge then becomes the trailing edges of subsequently cut sheets that are wound about the mandrel into tubes with the enhanced pliability rendering the edge more conformable and adhesively securable to the outer surface of the tube.
While skivers have proven somewhat successful in the fabrication of convolutely wound tubes, they nevertheless have had inherent problems and shortcomings of their own. The paperboard material abraded away by the skiver, for example, typically takes the form of a fine paper dust that must be collected and discarded by means of large and expensive cyclone type vacuum systems coupled to remove paperboard dust from the skivers to satisfy EPA standards. In addition, since finished tubes are graded by weight, discarding the paper dust is tantamount to discarding product itself and, after long periods of operation, can result in significant waste. Skivers can also produce high levels of noise during operation and in some instances can require special measures to insure that noise levels fall within OSHA standards. Further, the abrasive sanding belts of the skivers also tend to wear out, which necessitates down time of the tube winding system for belt replacement. Finally, if the paperboard being drawn from its supply roll becomes twisted or if the line is stopped for a significant time, the belt of the skiver can and often does sand completely through the paperboard material. This obviously generates waste and can even cause jamming of the paperboard at subsequent stations of the winding system.
Another attempt at rendering the trailing edge of paperboard sheets conformable to the tube contour has included mechanicaly deforming the trailing edges into a corrugated configuration prior to tube winding so that the corrugated edge can wrap about the contour of and can be adhesively secured to the finished tube. Such a technique is disclosed in U.S. Pat. No. 3,983,905 of Witzig. While this technique can be adequate, it nevertheless has proven to be an incomplete solution. The corrugated shape of the trailing edge, for example, can be unacceptable in instances where a smooth surfaces tube is required. Further, the alternating ridge and groove configuration of the corrugated trailing edge reduces the area of the trailing edge that becomes juxtaposed the facing surface of the tube and therefore reduces the available area of contact between the corrugated trailing edge and the tube so that the adhesive tend to be only marginally sufficient to secure the edge to the tube. As a result, the edge can and sometimes does pull away from the tube to create an undesirable flap that can interfere with use of the tube.
Thus, it is seen that a continuing and heretofore unsolved need exists for an improved system of fabricating convolutely wound tubes from paperboard sheets that insures conformability and securability of the trailing edges of the sheets to the outer surface of the tubes while avoiding the inherent problems and shortcomings of prior art systems as discussed hereinabove. It is to the provision of such a system that the present invention is primarily directed.